<Communication and Broadcasting>
Communication is a term collectively referring to an action of transmitting, receiving, and exchanging information, such as symbols, audio, and video, between two points or between two more points. Among other things, Power Line Communication (PLC) is a technique for loading voice and data on a power signal and communicating the voice and data through a power line for supplying electric power.
As a concept contrasted with communication, there is broadcasting. The term broadcasting means that several pieces of information, such as entertainments, information, and education, are propagated to many and unspecified persons who have adequate receiving devices so that they can see or hear the several pieces of information at the same time.
An invention to be disclosed in the present invention can be defined as Power Line Broadcasting (PLB) in that a small amount of data is transmitted unidirectionally and received by many and unspecified persons. Among other things, the present invention relates to a transmission/reception apparatus and method in which time broadcasting information is loaded on the power signal of a power line and transmitted to a variety of devices, and it can be defined as Power Line Time Broadcasting (PLTB).
The power line broadcasting, unlike power line communication, enables long-distance transmission through a power line using a low frequency. It can achieve an object more effectively as compared with the existing power line communication when the object is to transfer information unidirectionally.
A concept and a technique of the above-described power line broadcasting needs to be introduction because of the following reasons inherent in the power line communication.
The power line communication (i.e., wired communication) uses a power line as a medium and thus has a possibility that it can affect other radio equipment because of the leakage of electric waves. A frequency band used to send and receive a large amount of data may be a frequency band limited by electric wave regulations in some cases.
Furthermore, the power line used in the power line communication is not a communication line composed of single equipment for a single purpose, like a telephone line or an Asymmetric Digital Subscriber Line (ADSL), but connected to various devices, such as house refrigerators, TV, and measuring equipment in Korea Electric Power. Thus, the power line used in the power line communication is inappropriate for a data communication line because of a very high noise level and the distortion or frequent disconnection of a signal. In particular, the power line must overcome special environments, such as a high load, an interference phenomenon, shifting impedance, and a signal attenuation phenomenon, and transfer data through limited signal power.
<Necessity of Time Information Broadcasting>
Today, time is a physical quantity for the most accurate measurement. For its accuracy, time information is worthy to be sufficiently utilized in the entire industry. Therefore, to manage and accurately maintain the time information becomes important for the utilization.
Regarding the time information, standard times managed and maintained by respective countries, in addition to International Atomic Time (TAI) and Coordinated Universal Time (UTC), are broadcasted in the form of long waves. Furthermore, a reference time of an atomic clock mounted on a Global Positioning System (GPS) satellite is used as the time information.
Standard frequency broadcasting can be received by a simple shortwave and longwave radio receiver and has thus been widely used. A time frequency can be corrected at shipping, a spot where communication and electronic equipment for military communication is used, etc.
However, shortwave band signal is difficult to receive indoors because it chiefly uses a space wave, and it has a disadvantage, such as a deterioration of the reception sensitivity according to the state of an ionization layer and a place where a receiving antenna is installed.
Furthermore, a method of acquiring time information, such as standard time information, using an Internet network or a telephone network is indirect and limited to some degree in supplying the time information to various electronic products and various instruments within factory facilities and research institutes.
Accordingly, there is a need for a technique for broadcasting and sending time information using a power line, which can send the time information (e.g., radio time broadcasting and a reference time using a GPS) without additional dedicated lines and can use the existing electric equipment without change and which can be used to execute home automation devices and can be used in industry fields where various instruments or system equipment is installed and various businesses in line with national and civilian policies.